This invention relates in general to a process for sealing soil formations. More particularly, this invention relates to a novel process for sealing soil formations, especially for sealing the base of a dump or for encapsulating old pollution sources or dumps, using sludge, such as sewage sludge or river mud.
There have recently been substantial problems in disposing of wet sludge. For example, large quantities of wet sludge are obtained each year in removing mud from seaports. Such mud is often contaminated with heavy metals. Before disposing of this sludge, it is common to partially dry the sludge, optionally after adding flocculants, by means of traveling screen presses, thereby forming a soft plastic material with water content between 55-80%, based on the dry solids.
This waste material must usually be stored in sealed dump areas, depending on the pollution content of the sludge. Such sludge is primarily classified in waste dump class II, and in some cases in waste dump class III. Such waste dumps must be provided with a special seal to protect the soil and ground water. To achieve the required waste dump properties, the natural soil formation of the planned dump site must be sealed by means of a special process. But, the coefficients of permeability to be achieved by such sealing measures have become increasingly stricter. Consequently, the disposal of sludge in sealed waste dumps is expensive, particularly as a result of the following two factors: (1) a soft sludge mass cannot be dumped without additives, because the sludge lacks stability and load bearing capacity; and (2) large quantities of sludge require a larger and more expensive dump area, using up area that could be used for other materials. This latter factor is of special interest because new dumping areas will be available only to a limited extent in the future.
Thus, while sewage sludge is a waste product that is available almost everywhere and is also inexpensive, disposal by incineration or dumping in sealed waste dumps is expensive. As a consequence, there is a need for different types of disposal of sludge.
In the past, one use developed for sewage sludge obtained from waste water treatment facilities has been for sealing subsurface soil layers. European Patent B 125,680 describes such a process whereby the sewage sludge is used to seal subsurface soil layer of sand or gravel and sand against water. In this process, the sludge was rendered in a pasty or kneadable form by removing water, and mixed with the soil layer in a weight ratio of about 10-30%, based on the dry weight of the soil layer. The mixture is then mechanically compressed. A special use of this process is for sealing sand or gravel layers allowing soil above the sealing soil layer to be cultivated and watered, thus making permanent plantings in desert regions economically possible for the first time.
While adequate coefficients of permeability for many purposes can be achieved using the process described in European Patent B 125,680, a stronger sealing effect with a smaller coefficient of permeability is not necessary for the uses it disclosed, such as cultivation. However, the situation is different for waste dumps. There, the coefficient of permeability achieved by sealing methods must be much more stringent. Thus, in the past waste dumps have been sealed with clays, or sometimes plastic sheets. But, much better coefficients of permeability can now be achieved through the present invention, allowing mud or sewage sludge to be used to encapsulate, or seal, such dumps.
The problems enumerated in the foregoing are not intended to be exhaustive, but rather are among the many which tend to impair the effectiveness of previously known processes. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that processes appearing in the art have not been altogether satisfactory.
Recognizing the need for an improved process, it is therefore a general object of the present invention to provide a novel process for sealing soil formations, especially for sealing the base of waste dumps or encapsulating waste dumps and old pollution sources, by using sewage sludge or river mud, thus minimizing or reducing the problems of the types previously noted.
It is a further object of the present invention to provide a novel process for using sludge or mud as a construction material for sealing the base or encapsulating the surface of existing dumps in collecting basins for contaminated water, instead of simply disposing of the sludge or mud.
It is a further object of the present invention to provide a novel process for sealing soil formations which achieves a much better coefficient of permeability than processes previously noted.
It is a further object of the present invention to provide a novel process for sealing soil formations with a non-hardening seal.